The present invention generally relates to safety devices for mitigating the danger posed by the presence of flammable vapors in proximity to a gas-burning appliance and more particularly pertains to a control system that shuts down the operation of the appliance when the presence of flammable vapors is detected.
A potential hazard inherent in the operation of a gas-burning appliance is that it may cause flammable vapors to ignite that happen to collect in and around the appliance. Ignition may either be caused by the burner or pilot flame or by an electric or electronic ignitor upon being energized. This is especially problematic in for example water heaters or furnaces that are located in garages in which cars are parked where the leakage or spillage of gasoline may occur. Once a combustible mixture reaches the appliance, a fire or explosion may result.
Efforts to address this potential safety hazard have been previously directed to ensuring adequate ventilation in and around the appliance, the elevation of the appliance in an effort to distance it from flammable vapors that are denser than air, and more recently, the isolation or sealing of the burner from its surroundings. Attempts have also previously been made to adapt specialized sensors for the purpose of sounding an alarm in the event the presence of certain flammable vapors is detected. Such systems are however incapable of automatically and positively preventing the ignition of flammable vapors by a gas-fired appliance. Moreover, a gas-fired appliance that relies on an automatic ignition system poses an additional hazard as merely shutting off the supply of gas so as to extinguish the burner would not necessarily preclude ignition by an electronic or electric ignitor should it subsequently become energized.
A flammable vapor control system is needed that is able to mitigate the danger of a gas-burning appliance that employs an automatic ignition system so as positively prevent such appliance from igniting flammable vapors. Such system must be capable of reliably removing all potential ignition sources once a certain concentration of flammable vapors has been detected.
The present invention overcomes shortcomings of previously known approaches for mitigating the dangers associated with a gas-burning appliance. By employing a microprocessor that controls the operation of a gas appliance both in terms of regulating the flow of gas to the appliance as well as controlling the operation of the ignition system, a system is provided that positively precludes the ignition of flammable vapors by the appliance. The microprocessor is responsive to a sensor that is capable of detecting the presence of flammable gases. Once a sufficient concentration of flammable vapor is detected, the flow of gas to the appliance is shut off to extinguish both the burner as well as an associated pilot flame if present, and if the appliance employs a hot surface igniter or spark igniter, the ignition system is de-energized. By causing the microprocessor to respond to a concentration of flammable vapors well below a combustible concentration, a substantial margin of safety is automatically built into the system.
The system may additionally control the operation of an induced draft fan that is activated whenever the gas valve is energized and may additionally be activated during a pre-purge or post-purge cycle to clear the combustion chamber of any flammable vapors
The flammable vapor sensor is connected to the microprocessor through suitable interface circuits. The sensor changes resistance as a function of the presence of flammable vapors wherein the resistance increases along with an increase in the vapor concentration. The microprocessor measures the resistance of the sensor and the response is triggered at a preselected resistance. The system is readily adaptable to a variety of gas-fired appliances including, but not limited to, furnaces and water heater systems.
More particularly, the present invention provides for the interconnection of a flammable vapor sensor to a microprocessor having an internal analog-to-digital converter. The control will monitor the resistance of the sensor, and when it detects the presence of a preselected concentration of flammable vapors, the controller will de-energize both the gas valve and the ignition source. The controller may monitor the sensor resistance at all times or it may alternatively, only at the beginning and during an ignition cycle. Another optional feature includes the ability to lock out at a given vapor in a volatile lockout which would require the removal and subsequent re-application of power. As a further alternative, a non-volatile lockout can be employed which cannot be reset by simply removing and re-applying power. Such feature may be used in combination with the volatile lockout wherein the non-volatile lockout becomes active after resetting the volatile lockout a predetermined number of times. As a further alternative, the system may include a fuse which blows when a predetermined level of flammable vapors is sensed by the sensor.
These and other features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment which, taken in conjunction with the accompanying drawings, illustrates by way of example the principles of the invention.